Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which is connected to an external electric power source through lead portions and pad electrodes to receive a high voltage required for accelerating the electron beams.
Description of Related Art
Generally, electron emission devices are classified into a first type where a hot cathode is used as an electron emission source, and a second type where a cold cathode is used as the electron emission source.
Among the second type electron emission devices there is known a field emitter array (FEA) type, a surface conduction emitter (SCE) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a ballistic electron surface emitting (BSE) type.
The MIM-type and the MIS-type electron emission devices have a metal/insulator/metal (MIM) electron emission structure and a metal/insulator/semiconductor (MIS) electron emission structure, respectively. When voltages are applied to the metallic layers or to the metallic and the semiconductor layers, electrons are transferred and accelerated from the metallic layer or the semiconductor layer having a high electric potential to the metallic layer having a low electric potential, thereby providing the electron emission.
The SCE-type electron emission device includes first and second electrodes formed on a substrate while facing each other, and a conductive thin film disposed between the first and the second electrodes. Micro-cracks are made at the conductive thin film to form electron emission regions. When voltages are applied to the electrodes while making an electric current flow to the surface of the conductive thin film, electrons are emitted from the electron emission regions.
The FEA-typed electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the electron emission source when an electric field is applied thereto under a vacuum atmosphere. A front sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a carbonaceous material, such as carbon nanotube, graphite and diamond-like carbon, has been developed to be used as the electron emission source.
With the electron emission device using the cold cathode, first and second substrates form a vacuum structure, and electron emission regions and driving electrodes are formed at the first substrate. Phosphor layers and an anode electrode for accelerating the electrons emitted from the first substrate toward the second substrate are formed at the second substrate to provide the light emission or the image displaying.
In order to receive the high voltage required for accelerating the electron beams, the anode electrode is connected to an external electric power source via lead wires formed throughout the inside and the outside of the vacuum structure on the second substrate while receiving a direct current potential, and pad electrodes are formed external to the vacuum structure. When a large amount of current flow is transmitted to the anode electrode, a structure is used where a plurality of lead wires are arranged or the width of the lead wires is enlarged, in view of the resistance of the lead wires.
The first and the second substrates forming the vacuum structure are sealed to each other through a seal frit to prevent external air from being introduced into the vacuum structure. However, while the seal frit exerts excellent adhesion with respect to oxide film, glass, ceramic, or indium tin oxide (ITO), it does not with respect to chromium (Cr) used for the lead wires of the anode electrode. As a result, the vacuum state of the vacuum structure may be compromised.
This vacuum compromise phenomenon results because of the shortage of diffusion media for attaching the seal frit to chromium. In order to prevent such a phenomenon, a method of forming an oxide film or a black oxide film has been proposed. However, since such a film formation process is conducted at a high temperature exceeding the glass transition temperature (about 800-1100° C.), it is not preferable to conduct a film formation process with respect to the lead wires formed on the second substrate.